The present invention is generally directed to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions with certain morphologies. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toner compositions with an average volume diameter of from about 1 to about 25, and preferably from 1 to about 10 microns and narrow GSD of, for example, from about 1.16 to about 1.30, as measured on the Coulter Counter, can be obtained. Also, the morphology of the toner particles can be tuned, or preselected from like a bunch of grapes morphology through cauliflower, raspberries, potatoes to perfectly spherical particles. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment, and optionally a charge control agent or additive in an aqueous mixture containing an ionic surfactant in amount of from about 0.01 percent (weight percent throughout unless otherwise indicated) to about 10 percent and shearing this mixture at high shear with a latex mixture comprised of suspended resin particles of from, for example, about 0.01 micron to about 2 microns in volume average diameter, in an aqueous solution containing a counterionic surfactant in amounts of from about 0.01 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in an amount of from 0 percent to about 5 percent, thereby causing a flocculation of resin particles, pigment particles and optional charge control particles, followed by (a) stirring at from 250 rpm to 600 rpm, or (b) stirring assisted with heating from about 40.degree. C. to about 5.degree. C. below the resin Tg and preferably 20.degree. C. to 5.degree. C. below the resin Tg, or (c) shearing of the flocculated mixture, for example by attrition at 20 rpm to about 400 rpm, or (d) shearing assisted by heating of the flocculent mixture which is believed to form statically bound aggregates of from about 1 micron to about 10 microns in volume average diameter comprised of resin, pigment, and optionally charge control particles. The morphology of the aforementioned statically bonded aggregated particles can be controlled by adjusting the temperature in the aggregation stage (below the resin Tg), the time of the aggregation, and by the shear. By extending the time of the aggregation and/or increasing the temperature and/or applying the shear, one can more densely pack the submicron particles in the aggregated particles and as a result form more uniform toner particles. The reverse causes formation of the particles with higher fractal dimensions (loosely packed) which upon heating can form particles with some voids or holes. The formation of electrostatically bonded aggregates is followed by coalescence which comprises heating above the resin Tg. It is believed that during the heating stage the components of aggregated particles fuse together to form composite toner particles. The coalescence step (iv) can have an impact on the toner particle morphology. Factors, such as coalescence temperature, time of heating as well as melt flow properties of the polymeric resin, contribute to the toner particle morphology. By increasing the temperature of the coalescence and/or extending the time of heating, the morphology of toner particles can be tuned from "bumpy" structures to smooth surfaces. The morphology can also depend on the melt flow properties of the resin, which is closely related to the type of resin, its molecular weight, Tg, degree of crosslinking, presence of plasticizer, and the like. Also, by increasing the melt flow properties of the polymeric resin, the morphology of the particles can be changed from "bumpy" to smooth and spherical as illustrated herein. In another embodiment thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkmann Polytron, a microfluidizer or a sonicator, thereafter shearing this mixture with a latex of suspended resin particles, such as poly(styrenebutadiene acrylic acid), poly(styrenebutylacrylate acrylic acid) or PLIOTONE.TM. a poly(styrene butadiene), and which particles are, for example, of a size ranging from about 0.01 to about 0.5 micron in volume average diameter as measured by the Brookhaven nanosizer, in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., and nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which on further stirring for 1 to about 24 hours, or further stirring while heating or shearing, for example, using the attritor, or shearing while heating, for example, from about 25.degree. C. to about 50.degree. C. results in the formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Multisizer II) with a morphology ranging from a bunch of grapes, loosely or densely packed, to flakes where the morphology of the aggregates can be controlled by temperature, shear, and time. Thereafter, heating about 5.degree. C. to about 50.degree. C. above the resin Tg, which Tg is in range of from about 50.degree. C. to about 80.degree. C., to provide for particle fusion or coalescence of the polymer and pigment particles with the morphology controlled by the temperature of coalescence, the time of coalescence and the melt flow properties of the resin; followed by washing with, for example, hot water to remove surfactant, and drying toner particles comprised of resin and pigment with various particle size diameters can be obtained such as from 1 to 12 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present.
While not being desired to be limited by theory, it is believed that the flocculation or heterocoagulation is caused by the neutralization of the pigment mixture containing the pigment and cationic surfactant absorbed on the pigment surface with the resin mixture containing the resin particles and anionic surfactant absorbed on the resin particle. Depending on the conditions of this flocculation step such as time, shear and temperature, submicron resin particles and pigment particles will pack in the aggregate more densely or loosely and this will be a factor contributing to their final morphology. Thereafter, heating the aggregates, for example 5.degree. C. to 80.degree. C. above the resin Tg, fuses the aggregated particles or coalesces the particles to enable toner composites of polymer and pigments and optionally charge control agents. The temperature of the coalescence as well as the time for which the aggregated particles were heated above their Tg (step iv) will effect the morphology of the final toner particles, ranging from a bunch of grapes type of morphology to perfectly spherical. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the pigment mixture contains the pigment particle and anionic surfactant, and the suspended resin particle mixture contains the resin particles and cationic surfactant; followed by the ensuing steps as illustrated herein to enable flocculation by charge neutralization while shearing, and thereby forming statically bound aggregate particles by stirring and heating (below the resin Tg), and thereafter, that is when the aggregates are formed, heating above the resin Tg to form stable toner composite particles.
Of importance with respect to the processes of the present invention in embodiments is controlling the shear time, shear rate and shear temperature, and the aggregation temperature and time since these factors can primarily contribute to the morphology of the aggregated particles and cause more densely or more loosely packed aggregates. Control of the temperature and the time of the coalescence or heating above the resin Tg (step iv) is of importance since these factors can effect the morphology of the final toner particles significantly; by increasing from about 1 hour to about 4 hours the temperature from about 5.degree. C. to about 50.degree. C. above the resin Tg, and/or the time of coalescence from about 1 hour to about 4 hours, the morphology of the particles can be tuned from "bumpy" to smooth. Another factor that can effect the morphology of the toner particles is the melt flow properties of the aggregated resin with increasing, from about 2 to about 10 grams per 10 minutes, the melt flow properties of the resin the surface of the toner particles can be changed from "bumpy" to smooth spherical. One factor contributing to the melt flow is the type of resin, for example polyester, polystyrene/butadiene, or polystyrene/acrylate, the molecular weight of the resin, the Tg, the degree of crosslinking and the presence of plasticizers like polyvinylbuturyal in an amount of from about 1 weight percent to about 20 weight percent.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with, for example, an average volume particle diameter of 3 to 11 microns and preferably less than about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.16 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized, such as pictorial color applications, small particle size colored toners of from about 3 to about 9 microns are desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130 .degree. C. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present, such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes, such as from about 1 to about 7 microns, and with higher pigment loading, such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures, such as from about 120.degree. C. to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, when a low gloss image of preferably from about 1 to about 30 gloss is desired, low gloss paper is utilized, such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and which after image formation with small particle size toners of from about 3 to about 5 microns and fixing thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, if higher image gloss is desired, such as from about over 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized, such as from about over 30 to about 60 gloss units, and which after image formation with small particle size toners of the present invention of from about 3 to about 5 microns and fixing thereafter results in a higher gloss toner image of from about over 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns such that the pile height of the toner layer(s) is considered low.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with very irregular shape with sharp edges, which may not be an optimum morphology from the charging and dry toner flow point of view. With the present invention, tuning of the toner particle morphology can be achieved to enable, for example, selected excellent morphologies desired for superior toner flow and excellent charging properties of the toner particles. Also, in conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized toner particles with an average volume particle diameter of from about 10 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7 result. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention, in embodiments small average particle sizes of, for example, from about 3 microns to about 9, and preferably 5 microns are attained without resorting to classification processes, and wherein narrow geometric size distributions are attained, such as from about 1.16 to about 1.30, and preferably from about 1.16 to about 1.25. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of the present invention in embodiments, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients, such as toner resin and pigment.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of the '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer such as acrylic acid in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group. In U.S. Pat. No. 4,983,488, there is disclosed a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. Similarly, the aforementioned disadvantages, for example poor GSD are obtained, hence classification is required resulting in low yields as illustrated in U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of oppositely charges are selected, and wherein flocculation as in the present invention is not disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other prior art that may be of interest includes U.S. Pat. Nos. 3,674,736; 4,137,188 and 5,066,560.
The process described in the present application has several advantages as indicated herein including the effective preparation of small toner particles with narrow particle size distribution with the desired morphology which can be tuned for particular xerographic applications.
In U.S. Pat. No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent, and a polyester and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising an halogenization procedure which chlorinates the outer surface of the toner and results in enhanced blocking properties. More specifically, this patent application discloses an aggregation process wherein a pigment mixture, containing an ionic surfactant, is added to a resin mixture, containing polymer resin particles of less than 1 micron, nonionic and counterionic surfactant, and thereby causing a flocculation which is dispersed to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites or toner compositions of from about 3 to about 7 microns in volume diameter and narrow geometric size distribution, as measured by the Coulter Counter, and which exhibit, for example, low fixing temperature of from about 125.degree. C. to about 150.degree. C., and image to paper gloss matching.
In U.S. Pat. No. 5,308,734, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant, adding thereto a counterionic surfactant with a polarity opposite to that of said ionic surfactant, homogenizing and stirring said mixture, and heating to provide for coalescence of said toner fine particles.
In U.S. Pat. No. 5,346,797, the disclosure of which is totally incorporated herein by reference there is disclosed a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in a water, which dispersion is comprised of a pigment, an ionic surfactant and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form electrostatically bounded toner size aggregates; and PA1 (iii) heating the statically bound aggregated particles above the Tg to form said toner composition comprised of polymeric resin, pigment and optionally a charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, an ionic surfactant and an optional charge control agent; PA1 (ii) shearing at high speeds the pigment dispersion with a polymeric latex comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, and a nonionic surfactant thereby forming a uniform homogeneous blend dispersion comprised of resin, pigment, and optional charge agent; PA1 (iii) heating the above sheared homogeneous blend below about the glass transition temperature (Tg) of the resin while continuously stirring to form electrostatically bound toner size aggregates with a narrow particle size distribution; PA1 (iv) heating the statically bound aggregated particles above about the Tg of the resin particles to provide coalesced toner comprised of resin, pigment and optional charge control agent, and subsequently optionally accomplishing (v) and (vi); PA1 (v) separating said toner; and PA1 (vi) drying said toner. PA1 (i) preparing by emulsion polymerization a charged polymeric latex of submicron particle size; PA1 (ii) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an effective amount of cationic flocculant surfactant, and optionally a charge control agent; PA1 (iii) shearing the pigment dispersion (ii) with a polymeric latex (i) comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form a high viscosity gel in which solid particles are uniformly dispersed; PA1 (iv) stirring the above gel comprised of latex particles, and oppositely charged pigment particles for an effective period of time to form electrostatically bound relatively stable toner size aggregates with narrow particle size distribution; and PA1 (v) heating the electrostatically bound aggregated particles at a temperature above the resin glass transition temperature (Tg) thereby providing said toner composition comprised of resin, pigment and optionally a charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent; PA1 (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution; PA1 (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); and PA1 (v) heating and coalescing from about 5.degree. to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. to about 90.degree. C. and preferably from between about 50.degree. and about 80.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent. PA1 (i) preparing a pigment dispersion, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent; PA1 (ii) shearing said pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant; PA1 (iii) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; and PA1 (iv) heating said bound aggregates above about the Tg of the resin. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, a counterionic surfactant with a charge polarity of opposite sign to the anionic surfactant of (ii) and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a latex comprised of resin, anionic surfactant, nonionic surfactant, and water; and wherein the latex solids content, which solids are comprised of resin, is from about 50 weight percent to about 20 weight percent thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and optional charge control agent; diluting with water to form a dispersion of total solids of from about 30 weight percent to 1 weight percent, which total solids are comprised of resin, pigment and optional charge control agent contained in a mixture of said nonionic, anionic and cationic surfactants; PA1 (iii) heating the above sheared blend at a temperature of from about 5.degree. to about 25.degree. C. below about the glass transition temperature (Tg) of the resin while continuously stirring to form toner sized aggregates with a narrow size dispersity; and PA1 (iv) heating the electrostatically bound aggregated particles at a temperature of from about 5.degree. to about 50.degree. C. above about the Tg of the resin to provide a toner composition comprised of resin, pigment and optionally a charge control agent.
In U.S. Pat. No. 5,370,463, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
In U.S. Pat. No. 5,344,738, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with a volume median particle size of from about 1 to about 25 microns, which process comprises:
In copending patent application U.S. Ser. No. 083,157, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
In U.S. Pat. No. 5,364,729, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising:
In copending patent application U.S. Ser. No. 083,116, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising
Toner particles with mechanical stability for extended time periods to withstand the development system in xerographic processes, and more spherical and more densely packed toner particles are desired. From a charging standpoint, a bumpy type of toner morphology is preferred and from a toner flow point of view, it is believed that spherical particles are preferable. These and other advantages are achievable with the processes of the present invention and more specifically these processes provide a method for the modification or tuning of the morphology of toner particles. This tuning of the morphology can be achieved by adjusting the processing conditions, such as temperature, time and shear, as well as selecting the proper polymeric materials with desired melt flow properties, such as about 20 to about 50 grams/10 minutes.